The present invention generally relates to operations performed in conjunction with a subterranean well and, in an embodiment described herein, more particularly provides multilateral wellbore junction isolation apparatus and associated well stimulation methods.
Wellbore junctions are formed at intersections of wellbores in a subterranean well. For example, a main or parent wellbore may have a branch or lateral wellbore drilled extending outwardly from an intersection between the main and branch wellbores. Of course, the main wellbore may extend below the intersection with the branch wellbore, for example, to intersect a formation from which it is desired to produce hydrocarbons into the main wellbore.
Unfortunately, however, some wellbore junctions are not able to withstand substantial internal pressure applied thereto. For this reason, pressure within these wellbore junctions is limited to the fracture gradients of the respective formations in which the wellbore junctions are positioned. Thus, if stimulation operations, such as fracturing, must be performed for formations downhole of the wellbore junctions, expensive, time-consuming and/or complicated procedures must be used to prevent exceeding the fracture gradients of the formations at the wellbore junctions. Moreover, if an acid fracturing stimulation method is being employed the wellbore junctions are also susceptible to corrosion damage from the fracturing acid if care is not taken to shield the junctions from such corrosive material.
Therefore, it would be quite desirable to provide apparatus and s methods for isolating a wellbore junction which are convenient and easily utilized, and which isolate the wellbore junction from fluid pressure applied through the junction, as well as the corrosive effects Of a fluid creating such pressure.
In carrying out principles of the present invention, in accordance with a preferred embodiment thereof, specially designed apparatus is provided for isolating a junction between first and second intersecting wellbores in a subterranean well. The apparatus is removably insertable in the well, in a single trip into the well, and is operative to create in the well a fluid flow passage sealingly straddling the junction and protecting the junction from a pressurized fluid, representatively a well treatment fluid such as a fracturing acid, forced into a portion of one of the first and second wellbores via the interior of a portion of the junction isolation apparatus.
In a preferred embodiment thereof, the junction isolation apparatus comprises an elongated generally tubular outer structure having first and second longitudinally spaced part upper and lower portions with first and second external sealing devices respectively disposed thereon, the second external sealing device having an outer surface through which a recess inwardly extends to the outer structure. An elongated generally tubular inner structure is coaxially, sealingly and removably received in the outer tubular structure, and a seal test fluid flow passage extends from the interior of the inner structure into the recess in the second external sealing device.
Preferably, the first external sealing device is a packer having unset and set orientations in which the packer respectively precludes and permits the removal of the inner tubular structure from the outer tubular structure, and the second external sealing device comprises a longitudinally spaced plurality of annular sealing members circumscribing a lower end portion of the outer tubular structure. The first sealing device may be of an alternative structure, such as a seal bore portion of the wellbore casing, if desired. Also, the packer could be replaced by a non-sealing type of support structure, such as a hanger, with the function of the first sealing device being performed by, for example, a bridge plug run prior to setting a whipstock used to deflect the isolation structure into the second wellbore, or a packer run in conjunction with the whipstock.
A lower end portion of the inner tubular structure is blocked by, for example, a plug structure or check valve, and upper and lower end portions of the inner tubular structure respectively carry third and fourth external sealing devices which slidingly seal against the inner side surface of the outer tubular structure and are positioned at the top and bottom of an annulus defined between the inner and outer tubular structures. A sidewall opening in the inner tubular structure, and a sidewall opening disposed in the outer tubular structure at the second seal device recess, communicate with the annulus. The annulus and these sidewall openings form the previously mentioned seal test fluid flow passage.
To ready the junction isolation apparatus for use it is lowered into the well, representatively on a suitable work string structure anchored to the inner tubular structure, in a manner sealingly engaging the second external sealing device with an interior area of a selected one of (1) a portion of the first wellbore downhole from the junction and (2) a portion of the second wellbore, and positioning the packer adjacent an interior area of the first wellbore uphole of the junction. By flowing a suitable pressurized test fluid downwardly through the work string and, via the test fluid flow passage, into the recess of the second sealing device the second sealing may be conveniently pressure tested before the packer is set.
Upon a successful completion of this seal pressure test, the packer is set, thereby releasing the inner tubular structure from the outer tubular structure, and the work string is pulled out of the well, thereby also removing the inner tubular structure from the outer tubular structure and withdrawing the inner tubular structure from the well. The outer tubular member is thus left in place within the well, with the interior of the outer tubular member defining a fluid flow path that, at its upper end, communicates with substantially the entire cross-sectional area of an upwardly adjacent longitudinal portion of the first wellbore, and at its lower end communicates with the interior of the selected wellbore portion. This fluid flow path straddles and is sealingly isolated from the wellbore junction.
A wellbore treatment process, for example a fracturing/stimulation process, may then be carried out by pumping a pressurized well treatment fluid, such as a fracturing acid, downwardly through the full cross-sectional area of the first wellbore portion extending upwardly from the upper end of the remaining outer tubular member and, via the fluid flow path extending through the interior of the remaining outer tubular structure, into the selected wellbore portion. During this acid fracturing stimulation process the pressurized fracturing acid is isolated from the junction, to prevent pressure and/or corrosive damage thereto, and there is no return circulation flow of the stimulation fluid being forced into the selected wellbore portion.
The configuration and placement of the remaining outer tubular structure permits, as noted above, the well treatment to be downwardly flowed directly through the first wellbore portion disposed above the outer tubular memberxe2x80x94i.e., through the entire cross-sectional area of such first wellbore portion. This advantageously reduces the pressure drop to which the flowing stimulation fluid is subjected and thus correspondingly facilitates higher stimulation fluid pumping rates. The configuration and construction of the overall isolation apparatus are quite simple, and the isolation apparatus may be installed in the well, and pressure-tested therein, with a single trip into the well. If the seal pressure test does not yield satisfactory results the entire isolation apparatus may be quickly and easily pulled out of the well for repair or refitting prior to the setting of the packer. After the stimulation or other well treatment process is completed, a suitable retrieval tool may be used to unset the packer and withdraw the outer tubular structure portion of the isolation apparatus from the well. Prior to its removal from the well the outer tubular member (when operatively extended into the second wellbore) may be conveniently utilized as a deployment tube through which a selected tool or other object may be lowered into the second wellbore to prevent interference between the lowered object and the junction area.
In an alternate embodiment thereof the junction isolation apparatus is provided with a modified outer tubular member having an enlarged upper longitudinal portion sized for coupling to a large diameter workstring which may be used to lower the junction isolation apparatus into the well, or be sealingly stabbed into the upper end of the outer tubular member after the junction isolation apparatus has been operatively positioned in the well by other means. During the stimulation process stimulation fluid is pumped downwardly through the workstring and operatively through the outer tubular member, thereby protecting the well casing from stimulation fluid pressure but still providing a substantially lowered stimulation fluid pumping pressure.